In situ combustion oil recovery method

ABSTRACT

Heavy petroleum may be recovered from an underground formation by in situ combustion followed by injection of a hydrocarbon, which may be produced petroleum which thermally decomposes into light, low viscosity liquids that readily flow toward producing wells and petroleum coke which deposits on the reservoir formation, thereby providing fuel for another in situ combustion and repeating the cycle of operation until substantially all of the immobile, heavy petroleum is converted into a low viscosity liquid and/or gas.

United States Patent 1191 Allen Aug. 20, 1974 IN SITU COMBUSTION OILRECOVERY METHOD Primary Examiner-Ernest R. Purser Attorney, Agent, orFirm-T. L. Whaley; C. G. Ries [75] Inventor: Joseph C. Allen, Bellaire,Tex.

[73] Assignee: Texaco Inc., New York, NY. [57] ABSTRACT 22] il d; N 171972 Heavy petroleum may be recovered from an underground formation byin situ combustion followed by [21] Appl' 307742 injection of ahydrocarbon, which may be produced petroleum which thermally decomposesinto light, low 52 us. 01. 166 261 viscosity liquid5 that readily flowtoward Producing 51 Int. Cl E2lb 43/16 wells and Petroleum coke whichdeposits on the reser- [58] Field of Search 166/260-263 voir formation,thereby Providing fuel for another in Y situ combustion and repeatingthe cycle of operation 5 References Cited until substantially all of theimmobile, heavy petroleum is converted il'ltO a 10W ViSCOSilZy and/0r3,072,187 1/1963 Carr 166/261 x 3,126,957 3/1964 McKinnell 166/261 X 7Claims, 1 Drawlng Figure T0 STORAGE fi w gc l 5 S I ,5 1 1% A A 2 Vi 1 i0 2 wusss16: ?f S\ "fiylf.Zgff,

Z .4 V 2w x hill I :j .j 7/ 52 215512? -;i 2 f.

I n l l "i h. 10-- j 3 13/ 1 Q a .1 "1" H iTy -rg qtv i I: L41), -1 iPATENTED 0020014 I J s BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to in situ combustion for the recoveryof petroleum from subterranean reservoirs.

2. Description of the Prior Art In recovery of petroleum fromsubterranean reservoirs, it usually is possible to recover only a minorportion of the petroleum in place by the so-called primary recoverytechniques, that is, those techniques which utilize only the naturalforces present in the reservoir. Thus, a variety of supplementalrecovery techniques have been developed in order to increase therecovery of petroleum in such reservoirs. In these supplementaltechniques which are commonly referred to as secon- IN SITU COMBUSTIONOIL RECOVERY METHOD I dary recovery operations, although they may betertiary in sequence of employment, energy is supplied to the reservoiras a means of moving the fluid within the reservoir to suitableproduction wells through which they may be withdrawn to the surface ofthe earth.

Secondary recovery techniques which are showing increasing promise arethose which involve in situ combustion. In an in situ combustionprocess, a portion of the carbonaceous material within the reservoir isburned or oxidize in situ in order to extablish a combustion front. Thecombustion front may be moved through the reservoir by either a director inverse drive. In a direct insitu combustion process the combustionis initiated adjacent to one or more injection wells and the resultingcombustion front is advanced through the reservoir in the direction ofone or more production wells by the introduction of a combustionsupporting gas through the injection well or wells. The combustion frontis preceded by a high temperature zone commonly called a retort zone,within which the reservoir petroleum is heated to affect a viscosityreduction and is subjected to distillation and cracking. The hydrocarbonfluids resulting from subjecting the petroleum to such a process aredisplaced to the production wells where they are withdrawn to thesurface of the earth. In an inverse combustion drive, the combustionfront is established adjacent to the production well or wells. As thecombustion supporting gas is introduced through the injection well, thecombustion front advances counter-currently to the flow of such gas inthe direction of the injection well. The in situ combustion procedure,whether inverse or direct, is particularly useful in the recovery ofthick heavy oils (petroleum) such as viscous petroleum crude oils andthe heavy tarlike hydrocarbons present in tar sands. While these tarlikehydrocarbons may exist within the reservoir in a solid or semi-solidstate, they undergo a sharp viscosity reduction upon heating and in anin situ combustion process they behave somewhat like the moreconventional petroleum crude oil. In situ combustion also may beemployed in the recovery of hydrocarbons from oil shale.

After in situ combustion has propagated through the formation, a largequantity of heat is stored in the formation matrix. It has previouslybeen found that the efficiency of the overall process may be improved bywater injection following in situ combustion which scavenges the heatfrom the hot reservoir rock, transporting it in the form of steam andhot water through the combustion zone and heating the formation ahead.My process scavenges the heat from the hot reservoir rock withhydrocarbons which may be, for example, crude petroleum oil whichdecomposes forming some oil solvent which vaporizes, transports heat andreduces oil viscosity ahead by both heat and dilution actron.

Heavy oils and'bitumen from tar sands yield quantities of petroleum cokewhen refined. This material has been used as fuel but has thedisadvantage of pulverizing and requires special handling equipment andburners. The produced bitumen from mining operations of the tar sands isfed to a coke still. However, all of the coke is not used. The excesspresents a problem of rendering the area unsightly. In fact,governmental regulations often require burying and improving the scenerywith plants. Most every refinery produces coke which has a relativelylow commercial value.

I propose a procedure for eliminating the need for coking the productionof oil at the surface. The coke, in the process of my invention, isgenerated in the formation which provides cost reduction and improvedefficiency.

SUMMARY OF THE INVENTION The invention is a process for the recovery ofhydrocarbons from a subterranean reservoir penetrated by spacedinjection and production wells. The method involves introducing acombustion supporting gas into the reservoir and igniting the gas andhydrocarbons in the reservoir in order to propagate a combustion frontbetween the injection and production wells, then producing hydrocarbonsthrough the production well or wells. After this in situ combustionoperation the injec tion of combustion supporting gasis terminated and aliquid hydrocarbon which may be crude petroleum oil is introduced intothe reservoir through the injection well; the crude oil then separatinginto gradations of light and heavy fractions upon contacting the hotreservoir. The lighter fractions proceed through reservoir to theproduction well while the heavier fractions including for example, coke,deposit upon the reservoir matrix to provide the fuel for a repeat ofthe in situ combustion operation.

The invention also embodies using a reservoir to upgrade petroleum fromany source by having it follow an in situ combustion operation. As thepetroleum contacts the hot reservoir it will separate into light andheavy fractions and the lighter, more desirable fractions are produced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may becarried out utilizing any suitable injection and production system. Theinjection and production systems may comprise one or more wellsextending from the surface of the earth into the subterranean reservoir.Such injection and production wells may be located and spaced from oneanother in any desired pattern. For example, a line drive pattern may beutilized'in which a plurality of injection wells and a plurality ofproduction wells are arranged in rows which are spaced horizontally fromone another. Exemplary of other patterns which may be used are thesocalled circular drive patterns in which the injection system comprisesa central injection well and the production system comprises a pluralityof production wells spaced about the injection well. Typical circulardrive patterns are the inverted five spot, seven spot, and nine spotpatterns. The above and other patterns are well known to those skilledin the art and for a more detailed description of such patternsreferences made to Uren, L.C,, Petroleum Production Engineering-OilField Exploitation, Second Edition, McGraw, Hill Book CompanyIncorporated, New York and London, 1939. While the well patternsdescribed in Uren are with reference to water flooding operations, itwill be recognized that such patterns are also applicable to theprocedure described herein.

In general, response to conventional, thermal oil recovery techniques isinherently slow. This presents a rather severe problem in remote areaswhere a pipeline and/or site refinery are needed for transporting andupgrading the crude. As high as 100,000 barrels of oil per day arerequired for economic operation of a surface upgrading plant andpipeline. Since it is impossible to initiate a project at aninstantaneous rate of 100,000 barrels per day, surface storage or trucktransport of the interim produced oil would be necessary but oftenprohibitively expensive. My scheme uses the formation itself for storageof produced petroleum crude oil, simultaneously upgrading it to thepoint which it is easily transferable via pipelines even in coldclimates. This feature would grossly reduce refining construction andoperating costs. The Athabasca tar sands of Canada are an example of alikely candidate for-the method of my invention. Construction andoperating costs in the field are much higher than in many other areassince transportation by pipeline is necessary and the upgraded crudecould be pumped through the pipeline. Having a refinery in a moredesirable location would result in a decided improvement in overalleconomics.

The method of my invention could be used in any oil recovery operationwherein the oil must be upgraded to a higher API gravity or lowerviscosity before it may be transported by pipeline. Although myinvention is not limited to such use it is evident that a mostconvenient and likely use of the process of the invention will be forheavy oils especially in cold climates. Crude oils of about API gravityand below are generally too viscous to transport via pipeline and wouldlikely be candidates for upgrading by the process of my invention. Itshould be recognized that this value is chosen for illustration only andis not intended to define limits to my invention.

In a typical embodiment of my invention the hydrocarbon to be injectedafter the in situ combustion step may be the crude oil produced from thesame reservoir. Using this technique the crude oil from a reservoir maybe recycled until it attains a desired APl gravity and/or viscosity andmay then be transported away. In another embodiment of my invention areservoir with particularly advantageous qualities for an in situcombustion operation may be used to remove coke and heavy ends from anycrude which requires such treatment. Thus, the use of surface treatmentfacilities to upgrade heavy crudes may be avoided.

The in situ combustion step in the process of my invention is carriedout by a conventional manner using known techniques. For example, acombustion supporting gas such as oxygen as contained in air, forexample, is injected into the injection well or wells and is forcedthrough the formation to the production wells. Next, ignition ofreservoir hydrocarbons and the oxygen is initiated and once combustionis attained the combustion front is propagated through the formationtoward the production wells. As this in situ combustion operationproceeds, the heat from the operation lowers to the viscosity of theinplace hydrocarbons which are moved toward the production wells wherethey are produced. After this in situ combustion step, the formation isleft with a great deal of heat energy from the combustion operation.Heretofore, after in situ combustion operations, a fluid such as waterwould be injected into the production wells where the heat stored in theformation would convert the water into steam which would then proceedthrough the reservoir producing more of the oil. However, in the methodof my invention the injection of hydrocarbons, preferably produced crudepetroleum, is initiated instead of water. Depending on the compositionof these hydrocarbons, they will then thermally decompose into agradation of products including gas, light low viscosity liquids thatreadily flow toward the producing wells and petroleum coke whichdeposits on the reservoir rock thereby providing fuel for another insitu combustion operation as previously described. This cycle may berepeated until substantially all of the immobile hydrocarbons, such ascoke, have been converted into a gas and/or low viscosity liquids byrecycling the produced crude, using it as the hydrocarbon to be injectedafter each in situ combustion step. Finally, after all the immobileheavy hydrocarbons are upgraded into a low viscosity liquid or gas, adisplacing fluid may be used to move the rest of the mobile fluids toproducing wells.

EXPERIMENTAL Pressure (p) 1,000 psia Temperature (T) 1,500F. in burnedout zone.

Porosity ((1)) 35 percent Oil Saturation (S0) percent Basis ofcalculations 1 Barrel (B) oil Specific heat of reservoir rock 36 BTU/ft./F.

Minimum thermal decomposition temperature of crude oil 900F.

Rock Volume:

B ftf /B Available heat in volume of reservoir occupied by one barrel ofoil in the reservoir (Specific heat of reservoir) X (Volume occupied byone barrel of oil) X (Temperature of reservoir after in situ combustionminimum thermal decomposition temperature of crude oil).

Degree of crackinggfil; Available heat X 100 Heat required BTU/Lb. Lb./B

Thus the available heat is over twice the heat necessary to thermallydecompose the quench oil.

In full scale operation the produced crude will be upgraded in situ. Onemethod of operation would be to re-inject all produced crude that hadnot been upgraded to a chosen degree. The upgraded property critical forshipping, could be density (higher API) or viscosity (lower value). Thechosen value would be dictated by surface refinery requirements oradequately low viscosity for transportation by pipeline.

Full scale operation as herein described would eliminate surface cokestilling of the produced heavy oil such as the bitumen from tar sands,and substituting for expensive and bulky surface vessel an undergroundcoking vessel, the hot reservoir rock. Steel vessels would beeliminated. Better thermal efficiencies would be experienced due to theexcellent insulating properties of the adjacent beds.

The present invention may be more fully understood by reference to theattached FIGURE which depicts a typical embodiment of my inventionduring operation. Petroleum bearing reservoir 10 is penetrated by aninjection well 11 and a production well 12. The wells are incommunication with the reservoir 10 by openings 13 in the wells. An insitu combustion front 14 is proceeding through the reservoir areabetween the wells. This in situ combustion front was begun by injectingan oxygen containing gas through the line 15 into the injection well 11.The hydrocarbons in the reservoir are ignited by conventional techniquesand injection of oxygen containing gas is continued. Ahead of the insitu combustion front 14 is an area 16 of petroleum and gaseouscombustion products. The in situ combustion raises the temperature ofthe reserovir and lowers the viscosity of the petroleum in area 16moving it toward production well 12 where it is removed. This petroleumis stored at the surface for injecting later. Whenever adequate heat hasbeen added to the reservoir matrix for thermally decomposing theproduced oil, air injection is terminated and petroleum is injected viawell 11 through line 17. The petroleum thus injected enters thereservoir in area 18 behind the in situ combustion front 14. Area 18 hasbeen raised to a high temperature by the in situ combustion front 14. Asthe injected petroleum encounters this hot reservoir thermal crackingtakes place whereby the overall average molecular weight of thepetroleum is lowered. Very heavy portions of this petroleum, such ascoke, deposit on the reservoir formation. The lighter portions of thepetro- Degree 228% leum proceed through the formation toward theproduction well 12. Air injection is resumed and the heavy coke-likethermal decomposition products are ignited by conventional techniquesand the process is re- 5 peated.

I claim: I

1. In the recovery of hydrocarbons from a subterranean reservoirinitially containing hydrocarbons of 15 API gravity or less penetratedby spaced injection and 10 production wells, the method comprising:

a. introducing a combustion-supporting gas into the reservoir,

b. forcing said gas from the injection well to the production well,-

c. igniting the hydrocarbons in the reservoir in order to propagate acombustion front to travel from the injection well to the productionwell,

d. producing hydrocarbons through the production well,

e. terminating the injection of the combustionsupporting gas into thereservoir,

f. injecting the hydrocarbons produced in step (d) into the injectionwell so that the hydrocarbons will separate into gradations of light andheavy fractions while in contact with the heated reservoir wherein aportion of the heavy fractions deposit on the reservoir matrix, and

g. producing the light fractions of the hydrocarbon.

2. A process as in claim 1 wherein the heavy fraction 3. A method ofremoving coke from petroleum which comprises:

a. introducing a combustion-supporting gas into a 40 subterraneanreservoir containing hydrocarbons penetrated by spaced injection andproduction wells,

b. forcing said gas from the injection well to the production well,

c. igniting the hydrocarbons in the reservoir in order to propagate acombustion front to travel from the injection well to the productionwell,

d. producing hydrocarbons through the production well,

. terminating the injection of a combustionsupporting gas into thereservoir,

f. injecting the hydrocarbons produced in step (d) into the injectionwell so that the hydrocarbons will separate into gradations of light andheavy fractions upon contacting the heated reservoir wherein coke isdeposited on the reservoir matrix, and

g. producing the lighter fractions of the injected bydrocarbons.

4. The method of claim 3 wherein the injected petroleum has an initialAPI gravity of 15 or less.

5. A process as in claim 3 wherein the coke deposited on the reservoirmatrix in step (f) is used as fuel for an in situ combustion process toagain heat the reservoir and the light fraction from step (g) isreinjected into the heat reservoir to remove additional coke.

6. In a process wherein a throughput in situ combustion operation hasraised the temperature of the formaprovement which comprises:

' a. reinjecting said petroleum into the reservoir after the in situcombustion operation so that the petro- 8 reservoir, and b. producingthe light fractions. 7. The process of claim 6 wherein the crude oil hasleum will separate into gradations of light and an initial API gravityof150011655- heavy fractions while in contact with the heated

2. A process as in claim 1 wherein the heavy fraction deposited on thereservoir matrix in step (f) is used as fuel for an in situ combustionprocess to again heat the reservoir and the light fraction from step (g)is reinjected into the heated reservoir to further upgrade it.
 3. Amethod of removing coke from petroleum which comprises: a. introducing acombustion-supporting gas into a subterranean reservoir containinghydrocarbons penetrated by spaced injection and production wells, b.forcing said gas from the injection well to the production well, c.igniting the hydrocarbons in the reservoir in order to propagate acombustion front to travel from the injection well to the productionwell, d. producing hydrocarbons through the production well, e.terminating the injection of a combustion-supporting gas into thereservoir, f. injecting the hydrocarbons produced in step (d) into theinjection well so that the hydrocarbons will separate into gradations oflight and heavy fractions upon contacting the heated reservoir whereincoke is deposited on the reservoir matrix, and g. producing the lighterfractions of the injected hydrocarbons.
 4. The method of claim 3 whereinthe injected petroleum has an initial API gravity of 15* or less.
 5. Aprocess as in claim 3 wherein the coke deposited on the reservoir matrixin step (f) is used as fuel for an in situ combustion process to againheat the reservoir and the light fraction from step (g) is reinjectedinto the heat reservoir to remove additional coke.
 6. In a processwherein a throughput in situ combustion operation has raised thetemperature of the formation above 900*F. while producing petroleum theimprovement which comprises: a. reinjecting said petroleum into thereservoir after the in situ combusTion operation so that the petroleumwill separate into gradations of light and heavy fractions while incontact with the heated reservoir, and b. producing the light fractions.7. The process of claim 6 wherein the crude oil has an initial APIgravity of 15* or less.